Bone anchoring device

ABSTRACT

An anchoring element includes a shank for anchoring to bone and a separate head that is connectable to the shank. The head has an exterior surface with a spherically-shaped section and an unthreaded tool engagement surface that is engageable with a drive tool when the head and the shank are connected to one another.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and the benefit of U.S.Provisional Patent Application No. 63/061,475, filed Aug. 5, 2020, thecontents of which are hereby incorporated by reference in theirentirety, and claims priority from European Patent Application EP 20 189703.0, filed Aug. 5, 2020, the contents of which are hereby incorporatedby reference in their entirety.

BACKGROUND Field

The application relates to a bone anchoring device which is generallyapplicable in orthopedic and trauma surgery, and more particularly inspine surgery.

Description of Related Art

In spine surgery, one or several motion segments of the spine can beconnected by a rod. The rod is anchored to the vertebrae using monoaxialor polyaxial bone anchoring devices. Such bone anchoring devicestypically include a bone anchoring element to be anchored, for example,in the pedicle of a vertebra, wherein the bone anchoring element, in thecase of a polyaxial device, is pivotably connected to a receiving part.The receiving part includes a recess for receiving the rod and afixation member to fix or lock the construct.

U.S. Pat. No. 6,835,196 B2, for example, describes a polyaxial boneanchoring device with a screw having a threaded section and a head witha spherical segment-shape, and a receiving portion for connecting thescrew to a rod. The thread section and the spherical segment-shaped headof the screw are separate parts. With such a device, it is possibleduring the application of the device to shorten the threaded section toa desired length before or after implanting, and then to connect thethreaded section to the head and the receiving portion.

In US 2008/0132957 A1, a bone anchoring device is described thatincludes a shank to be anchored in a bone or vertebra, a head, and areceiving part for receiving the head for connecting the shank to a rod.The shank and the head are separate parts, and so in use of the boneanchoring device, an appropriate shank can be selected depending on theparticular application and can be connected to the head for forming thebone anchoring device. In particular, shanks of different lengths can beprovided in combination with the head.

US 2014/0277158 A1 describes bone anchor assemblies having amulti-component bone anchor that is configured to allow the shank of thebone anchor to be bottom-loaded into a receiver member. One bone anchorassembly has a shank with a distal threaded portion and a proximal headportion, a ball having a spherical exterior surface and a central lumensized to receive the head portion of the shank, and a clip configured tobe engaged between the head portion and the ball, such that the clip isutilized to lock the ball in engagement with the shank.

SUMMARY

It is an object of the invention to provide a bone anchoring device thatpermits an improved or alternative way of treating various orthopedic,in particular spinal, disorders, conditions, and/or diseases, and/orwhich opens up additional options for the application of the boneanchoring device.

According to an embodiment, the bone anchoring device includes ananchoring element having a shank for anchoring in bone and a head, thehead having an exterior surface with a spherically-shaped section,wherein the shank and the head are separate parts configured to beconnected to each other, and wherein the head has a drive structure forengagement with a drive tool.

The drive structure has an enlarged size compared to known anchoringelements with ball-shaped heads. This permits screwing or otheradvancement of the bone anchoring element into bone with an increasedtorque.

In a further development, a receiving part for receiving the head andfor connecting the bone anchoring element to a rod is provided. Hence,the bone anchoring element and the receiving part may form a polyaxialbone anchoring device in which the shank can pivot at various anglesrelative to the receiving part and can be fixed at a particular angularposition. A pressure element may be provided to transmit the forceexerted by a fixation member to the head. Alternatively, the pressurecan be transmitted via the rod directly onto the head.

The shank also includes an engagement portion for a drive tool.Therefore, it is possible to first insert the shank into the bone, andthereafter place the receiving part with the head assembled thereto ontothe shank. Since the shank can be inserted without being coupled to thereceiving part, the step of insertion may be better facilitated sincethe visibility and the available space at the implantation site areincreased. If a correction of the insertion depth of the shank isnecessary or the bone anchoring device has to be removed after headattachment, the drive structure of the head can be engaged and therequired step can be effectively carried out.

In a specific embodiment, the shank may have a large outer diameter. Theengagement portion of the shank may be also designed such as to permitthe application of high torques.

Moreover, the bone anchoring device is robust and the receiving partwith the inserted head is easily connectable to the shank.

In another way of use, the head and the shank can be assembled prior tocoupling the head to the receiving part.

Various heads with different drive structures can be combined with aparticular shank. Such different drive structures can be, for example, atorx-shaped drive structure or a Mortorq® drive structure. In addition,a modular system can be provided where various heads can be combinedwith various shanks of different lengths, different diameters, differentthreads or bone engagement structures, or differing in one or more otherproperties.

In a further specific embodiment, the bone anchoring device includes aposition indication structure that indicates a specific angular positionof the head with shank relative to the receiving part, such as a zeroangle position.

The bone anchoring device may also include a bone plate having a holewith a seat for the head of the bone anchoring element, and optionally,a locking member for locking the head in the hole.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows a perspective exploded view of a first embodiment of a boneanchoring device.

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state.

FIG. 3 shows a cross-sectional view of the polyaxial bone anchoringdevice of FIGS. 1 and 2, the cross-section taken in a plane extendingthrough a center of a receiving part and a center of a head andincluding an axis of a shank.

FIG. 4 shows a perspective view from a top of the shank of a boneanchoring element of the bone anchoring device of FIGS. 1 to 3.

FIG. 5 shows a side-view of an upper portion of the shank of FIG. 4.

FIG. 6 shows a top view of the shank of FIGS. 4 and 5.

FIG. 7 shows a perspective view from a top of the head of the boneanchoring device of FIGS. 1 to 3.

FIG. 8 shows a perspective view from a bottom of the head of FIG. 7.

FIG. 9 shows a top view of the head of FIGS. 7 and 8.

FIG. 10 shows a cross-sectional view of the head of FIGS. 7 to 9, thecross-section taken along line A-A in FIG. 9.

FIG. 11 shows a perspective view from a top of the receiving part of thebone anchoring device of FIGS. 1 to 3.

FIG. 12 shows a perspective view from a bottom of the receiving part ofFIG. 11.

FIG. 13 shows a top view of the receiving part of FIGS. 11 and 12.

FIG. 14 shows a cross-sectional view of the receiving part of FIGS. 11to 13, the cross-section taken along line B-B in FIG. 13.

FIG. 15 shows a perspective view from a top of a pressure member of thebone anchoring device of FIGS. 1 to 3.

FIG. 16 shows a perspective view from a bottom of the pressure member ofFIG. 15.

FIG. 17 shows a top view of the pressure member of FIGS. 15 and 16.

FIG. 18a shows a cross-sectional view of the pressure member of FIGS. 15to 17, the cross-section taken along line D-D in FIG. 17.

FIG. 18b shows an enlarged detail of FIG. 18 a.

FIGS. 19a to 19c show perspective views from above of steps of mountingthe head of the bone anchoring element to the shank.

FIGS. 20a to 20c show cross-sectional views of the steps shown in FIGS.19a to 19c , respectively, wherein the cross-sections are taken in aplane including the shank axis and the central axis of the head.

FIGS. 21a to 21e show cross-sectional views of steps of assembling thehead with a pressure member to the receiving part wherein FIG. 21c is anenlarged view of a detail of FIG. 21 b.

FIGS. 22a to 22d show cross-sectional views of mounting thepre-assembled receiving part with head and pressure member to the shank.

FIG. 23a shows a cross-sectional view of the bone anchoring device ofFIGS. 1 to 3, with the bone anchoring element in a pivoted position andthe rod not inserted.

FIG. 23b shows a cross-sectional view of the polyaxial bone anchoringdevice in the pivoted position of FIG. 23a , with the rod and a fixationmember inserted into the receiving part and with the pivot positionlocked.

FIG. 24 shows a cross-sectional view of a modified embodiment of thebone anchoring device with inserted rod and fixation member.

FIG. 25 shows a perspective view of an embodiment of a system includingthe shank and two exchangeable heads for forming a bone anchoringelement of the bone anchoring device.

FIG. 26 shows a perspective exploded view of a bone anchoring deviceaccording to a second embodiment.

FIG. 27 shows a perspective view of the bone anchoring device of FIG. 26in an assembled state.

FIG. 28 shows a perspective view from a top of a head of the boneanchoring device of FIGS. 26 and 27.

FIG. 29 shows a perspective view from a bottom of the head of FIG. 28.

FIG. 30 shows a top view of the head of FIGS. 28 and 29.

FIG. 31 shows a cross-sectional view of the head of FIGS. 28 to 30, thecross-section taken along line F-F in FIG. 30.

FIG. 32 shows a perspective view from a top of a receiving part of thebone anchoring device of FIGS. 26 and 27.

FIG. 33 shows a perspective view from a bottom of the receiving part ofFIG. 32.

FIG. 34 shows a top view of the receiving part of FIGS. 32 and 33.

FIG. 35a shows a cross-sectional view of the receiving part of FIGS. 32to 34, the cross-section taken along line G-G in FIG. 34.

FIG. 35b shows an enlarged view of a detail of FIG. 35 a.

FIGS. 36a to 36d show cross-sectional views of assembling the boneanchoring device of FIGS. 26 and 27.

FIGS. 37a to 37c show cross-sectional views of pivoting the boneanchoring element relative to the receiving part of the bone anchoringdevice of FIGS. 26 and 27, and locking the pivot position afterinsertion of the rod with the fixation member.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, a bone anchoring device according to a firstembodiment includes a bone anchoring element 1 that has a shank 2 and aseparate head 3. The bone anchoring element 1 is, via the head 3,pivotably coupled to a receiving part 5 that receives a pressure member6 for transmitting pressure exerted by a fixation member 7 onto the head3. A rod 100 is used to couple at least two bone anchoring devicestogether. The bone anchoring device is of the polyaxial type, whichmeans that the anchoring element can assume various angular positions ofthe shank axis relative to the receiving part, and can be locked in eachof these positions.

As depicted in greater detail in FIGS. 4 to 6, the shank 2 has a firstend 2 a and an opposite end 2 b, and a bone thread portion 21 on atleast a portion of its length. The bone thread is configured to engagebone. In the embodiment shown, the bone thread portion 21 extends overalmost an entire length of the shank from a tip 22 at the second end 2 bup to a neck portion 23. At the first end 2 a, an engagement portion 24is formed, which has an outer surface with a structure that isconfigured to be engaged by a drive tool, such as a star-like structure,a torx-like structure, or a polygonal outer contour. A maximum outerwidth of the engagement portion 24 may be smaller than a maximum outerdiameter of the bone thread portion 21. Hence, in this embodiment, theshank has a relatively large diameter. More specifically, a maximumouter diameter of the bone thread portion 21 may be greater than amaximum outer diameter of the head 3. The engagement portion 24 may belimited by a substantially cylindrical portion 25 that forms an annularring which may serve as a stop for the drive tool.

Referring to FIGS. 7 to 10, the head 3 has a first end 3 a and anopposite second end 3 b, and a spherical segment-shaped outer surface 30between the first end and the second end. The spherical shape is suchthat the outer surface 30 includes the greatest diameter E of the spherein a direction perpendicular to the central axis C which coincides withthe shank axis when the head 3 is mounted to the shank 2. Moreover, thedistance from the greatest diameter E to the first end 3 a may besmaller than the distance between the greatest diameter E and the secondend 3 b. More specifically, the axial height of upper portion of thehead 3, i.e., between the greatest diameter E and the first end 3 a, isas small as possible to still permit pivoting on the one hand, and toprovide sufficiently large space at the first end for a drive structure31 on the other hand. The drive structure 31 in this embodiment includesa recess extending in the axial direction from the first end 3 a to adistance beyond the greatest diameter E towards the second end 3 b. Therecess has an inner contour that has a star-like shape, morespecifically, a torx-shape that has six radially extending longitudinalgrooves 31 a that have rounded ends and are arranged at regulardistances. The distance of the outermost end of the grooves 31 a in theradial direction seen from the central axis C is such that the drivestructure 31 extends over substantially the entire surface at the firstend 3 a, leaving only a small rim 32 that extends to the outer sphericalsegment-shaped surface 30. With this design, the drive structure 31permits a more robust engagement of the head and the ability to apply anincreased torque to the shank 2.

At a distance from the first end 3 a, a circumferential groove 33 isformed in the outer spherical segment-shaped surface 30. The groove 33may extend fully around the central axis C. Moreover, the groove 33 maybe located closer to the first end 3 a than to the axial position of thegreatest diameter E. The depth of the groove 33 in the radial directionmay be such that the groove extends into the grooves 31 a of the drivestructure 31, as depicted in FIGS. 7 and 10.

At the second end 3 b, a counterpart engagement portion 34 is formed asa recess which is configured to receive the engagement portion 24 of theshank 2. In other words, the inner contour of the counterpart engagementportion 34 substantially matches the outer contour of the engagementportion 24 of the shank. Also, the depth of the recess forming thecounterpart engagement portion 34 corresponds substantially to the axiallength of the engagement portion 24. In addition, the recess has aslightly tapering inner wall that tapers and narrows towards the secondend 3 b. The drive structure 31 and the counterpart engagement portionmay be in communication with each other. A shoulder 34 a between therecess and the drive structure 31 forms a stop for the insertion of theengagement portion 24 of the shank.

The head 3 is at least partly flexible in a region adjacent the secondend 3 b. This is achieved by means of a plurality of longitudinal slits35 that are open to the second end 3 b and that extend at least up tothe greatest diameter E, preferably up to and into the circumferentialgroove 33. The number and width of the slits 35 is selected such thatthe head 3 exhibits in the lower portion adjacent to the second end 3 bsufficient flexibility to permit insertion of the engagement portion 24in a snap-on manner and to hold the engagement portion 24 in the recess.The tapered inner wall of the recess permits tight engagement of theengagement portion 24.

Referring to FIGS. 11 to 14, the receiving part 5 will be described ingreater detail. The outer shape of the receiving part 5 may besubstantially cylindrical. The receiving part has a first end or top end5 a, a second end or bottom end 5 b, and a passage 50 extendingcompletely through the receiving part 5 from the first end 5 a to thesecond end 5 b. The central longitudinal axis C coincides with thecentral longitudinal axis C of the head 3 when the head 3 is at a zeroposition in the receiving part 5. An opening 51 at the second end 5 bmay have a size such that at least a portion of the lower end of thehead 3 can extend therethrough. Adjacent to the second end 5 b, thepassage 50 forms an accommodation space for at least a portion of thehead 3. More specifically, adjacent to the second end 5 b, a seat 52 isformed for the head 3. The seat 52 may have a hollow spherical segmentshape that matches the spherical segment shape of the head 3. When thehead 3 is accommodated in the lower portion of the receiving partadjacent to the second end 5 b, the head is supported in the seat 52 andconfigured to pivot therein like a ball and socket joint. Any othershape of the seat that provides this function can also be implemented.

Adjacent to the seat 52, the passage 50 widens into a main section 53that has a substantially constant inner diameter. Starting from thefirst end 5 a, a substantially U-shaped recess 54 is formed, resultingin two free legs 55. The substantially U-shaped recess 54 forms achannel which is configured to receive the rod 100 therein. In addition,adjacent to the first end 5 a, an inner thread 56 is formed on the legs55 which is configured to cooperate with a fixation member 7, forexample a set screw. The inner thread may be of any thread type,preferably a thread type that reduces splaying of the legs 55, such as,for example, a square thread or flat thread. At the center of the legs55 in the circumferential direction, transverse through-holes 57 areformed in each leg, respectively. The through-holes 57 may be at anaxial position above a bottom of the substantially U-shaped recess 54and below the threaded portion 56. The through-holes 57 serve forreceiving pins 4 that are configured to extend completely through thethrough-holes 57 into the passage 50. At the lowermost end of the innerthread 56, a circumferential groove 58 or undercut is formed on each leg55 that provides, with its upper surface 58 a, an abutment for a portionof the pressure member 6. Additional tool engagement recesses 59 may beprovided in the outer surface of the legs 55, respectively.

Referring to FIGS. 15 to 18 b, the pressure member 6 has a first end 6 aand an opposite second end 6 b, and is configured to be arranged in thereceiving part 5 such that the second end 6 b faces towards the secondend 5 b of the receiving part. An upper portion 60 of the pressuremember 6 is substantially cylindrical such that it fits into thecylindrical portion 53 of the passage 50 in the receiving part and canmove therein in an axial direction to some extent. Hence the cylinderaxis C is coincident with the central longitudinal axis of the receivingpart 5 when the pressure member 6 is arranged in the receiving part 5.Two opposite legs 62 offset by 180° stand upright away from an uppersurface 61 of the cylindrical portion 60. The legs 62 may have flatinner walls facing each other and cylindrical outer walls correspondingto the shape of the cylindrical portion 60. At the first end 6 a, eachleg includes an outwardly protruding rim 63 that extends beyond theouter surface of the cylindrical section 60 in a radial direction. Thelegs 62 have a length and thickness such that they are flexible at leastpartially in the region of their free end and can be compressed towardseach other and resiliently move back to their straight position. Theupper surface of the protruding rim 63 forms the first end 6 a of thepressure member 6. In each leg 62, an axial elongate hole 64 is providedthat serves for receiving a portion of the pin 4.

The pressure member 6 is further configured to support the rod 100 andtherefore has a recess 65 that extends perpendicular to the cylinderaxis C of the cylindrical portion 60. The recess 65 forms a supportsurface for an inserted rod 100. The cross-section of the recess 65 maybe substantially V-shaped, as can be seen in particular in FIG. 18a ,preferably with a rounded bottom. By means of this, rods of differentdiameters can be safely supported so that they are substantiallyprevented from moving in a direction transverse to the rod axis. A bore66 that is coaxial with the cylinder axis of the cylindrical portion 60extends from the upper surface 61 of the cylindrical portion to thesecond end 6 b and provides access to the head 3 for a drive tool. As aconsequence, the inner diameter of the bore 66 is at least as large asthe greatest width of the recess with the drive structure 31 on thehead, so that a drive tool can engage the drive structure 31 when thedrive tool extends through the bore 66. At a distance from the secondend 6 b a substantially spherical segment-shaped recess 67 is formed,the shape of which matches the outer spherical shape of the head 3. Aheight of the spherical portion 67 in the axial direction is such thatwhen the head 3 is mounted to the pressure member 6 and to the receivingpart 5 and rests in the seat 52 of the receiving part in a zero angleposition of the shank 2, the upper portion of the head 3 between thegroove 33 and the first end 3 a lies within the spherical recess 67.Moreover, the spherical recess 67 and the seat 52 together form aspherical pivot support for the head 3, as can be seen in particular inFIGS. 23a to 24.

Between the spherical recess 67 and the second end, the pressure member6 includes an inner circumferentially extending protrusion 68 thatprotrudes inwardly towards the central axis C. The protrusion 68 is at aposition corresponding to and has a shape adapted to the position andshape of the circumferential groove 33 on the head 3 when the head 3extends into the spherical recess 67 of the pressure member. To enableeasier engagement with and disengagement from the groove 33, theprotrusion may be rounded. Moreover, when the head 3 is supported in theseat 52 of the receiving part 5, the protrusion 68 is configured toengage the groove 33. As the groove 33 as well as the protrusion 68extend perpendicular to the central axis C, the engagement is achievedwhen the head 3 is at a zero angle position of the shank relative to thereceiving part 5 (i.e., when central axes of the shank and the receivingpart are coaxial). The engagement can produce an audible or tactilefeedback. Therefore, the groove and the protrusion form a positionindication structure configured to indicate a specific position of theshank relative to the receiving part. In the specific example, thespecific position is the zero position where the shank 2 is coaxial withthe receiving part 5. Between the protrusion 68 and the second end 6 b,an outwardly tapering section 68 a may be provided that facilitatesinsertion of the head 3 into the pressure member 6. The outwardlytapering section 68 a may form a ramp for the head 3 when the headpivots so that the protrusion 38 can move easier move out of the groove33.

The outer surface 69 between the second end and up to a distance beyondthe spherical section 67 may be slightly tapered and narrows towards thesecond end 6 b, whereby a step 69 a may be formed. By means of this, awall thickness is slightly reduced so that the protrusion 68 can snapinto the groove 33 more easily.

The parts and portions of the bone anchoring device and of the rod maybe made of any material, preferably however, of titanium or stainlesssteel, or of any bio-compatible metal or metal alloy or plasticmaterial. For a bio-compatible alloy, a NiTi alloy, for example Nitinol,may be used. Other materials that can be used are magnesium or magnesiumalloys. Bio-compatible plastic materials that can be used may be, forexample, polyether ether ketone (PEEK) or poly-L-lactide acid (PLLA).The various parts can be made of the same or of different materials fromone another.

Mounting of the head to the shank will be described, referring to FIGS.19a to 20c . It shall be noted that the bone anchoring element can beused in many applications, so that the assembled bone anchoring elementcan be inserted as one piece in, for example, receiving parts ofpolyaxial bone anchors or bone plates with locking screws. As shown inthe figures, first, the head 3 is oriented such that the counterpartengagement portion 34 of the head 3 and the engagement portion 24 of theshank 2 are facing each other and the recesses are rotationally aligned(FIGS. 19a and 20a ). Then, the head 3 is pressed onto the engagementportion 24 of the shank 2 so that the lower portion of the head 3 in theregion of the recess 34 is spread apart to let the engagement portion 24enter (FIGS. 19b and 20b ). Then, the engagement portion 24 moves withinthe recess until it abuts with the end surface 2 a at the shoulder 34 aof the recess 34 a and the counterpart engagement portion 34 closesaround the engagement portion 24. The head 3 is now rotationally fixeddue to the form-fit engagement of the engagement portions of the shankand the head. In the axial direction, the shank 2 may be held to someextent by friction within the recess.

Steps of assembling the receiving part 5 with the pressure member 6 andthe head 3 are shown in FIGS. 21a to 21e . As shown in FIGS. 21a to 21c, the head 3 is inserted with the leading first end 3 a into thepressure member 6 from the second end 6 b thereof, until the protrusion68 of the pressure member 6 engages the groove 33 of the head 3. Thus,the protrusion 68 and the groove 33 provide a holding structure forholding the pressure member 6 and the head 3 together. Once assembled,the pressure member 6 and the head 3 are inserted from the first end 5 ainto the receiving part 5, with the second end 3 b of the head 3 facingtowards the opening 51. The rod recesses 54 and 65 of the receiving part5 and the pressure member 6 are aligned.

During insertion of the pressure member 6 with the head 3 assembledtherewith, the legs 62 of the pressure member 6 are slightly compressedtowards each other as the outer rim 63 abuts against the crests of theinner thread 56 of the receiving part 5. When the outer rim 63 is at thethread crest immediately above the groove 58, the elongate hole 64overlaps the through hole 57 and the pins 4 can be inserted, as shown inFIG. 21e . The pins 4 also form a securing structure against rotation ofthe pressure member in the receiving part. In this position, the head 3is in the accommodation space and not yet in the seat 52. This is theinsertion position which is defined at an uppermost position of thepressure member 6, in which the pressure member 6 abuts with the lowerend of the elongate hole 64 against a stop provided by the pins 4,respectively. Between the outer spherical surface 30 of the head 3 andthe seat, there is still enough space to allow for spreading of thelower portion of the head 3 to permit the insertion of the engagementportion 24 of the shank 2. the head may protrude slightly out of theopening 51.

Referring to FIGS. 22a to 22d , the mounting of the pre-assembledreceiving part, with pressure member 6 and head 3, to the shank 2 isshown. In FIG. 22a the engagement portion 24 of the shank 2 and thereceiving part 5 are rotationally aligned with respect to each other sothat the engagement portion 24 of the shank 2 can be inserted into therecess of the counterpart engagement portion 34 of the head 3 (FIG. 22b). As the lower portion of the head 3 is flexible, the lower portion canspread to permit the engagement portion 24 to enter. The pins 4 preventupward movement of the pressure member 6 during the insertion step. FIG.22c shows the step in which the engagement portion 24 has been fullyinserted into the recess of the counterpart engagement portion 34 andabuts against the shoulder 34 a.

Finally, as shown in FIG. 22d , the pressure member 6 is moved towardsthe second end 5 b of the receiving part so that the head 3 comes intocontact with the seat 52 of the receiving part and is supported there.Simultaneously, the outer rim 63 snaps into the groove 58. The uppersurface 58 a of the groove provides an abutment for the upper surface 6a of the pressure member at the legs 62 so that the head 3 is held inthe seat 52. The spherical recess 67 of the pressure member contacts aportion of the upper part of the head 3, so that the head 3 can be heldby friction in this position. Depending on the dimensions of the parts,this friction holding of the head 3 can be strong or weak. Preferably,the frictional force can be manually overcome by pivoting the receivingpart 5 relative to the head 3 and the shank 2. Simultaneously, the lowerportion of the head 3 is compressed in the seat 52 so that the headfirmly holds the engagement portion 24 of the shank.

As depicted in FIG. 23a , when the receiving part 5 is pivoted relativeto the shank 2, the protrusion 68 moves out of the groove 33 and allowsthe head 3 to pivot in the spherical seat 52 while also being held by aportion of the spherical recess 67. When the pivot position of the shank2 relative to the receiving part 5 is changed to the zero angleposition, i.e., the position in which the shank axis is coaxial with thecentral longitudinal axis C of the receiving part, the protrusion 68snaps into the groove 33, thereby producing an audible or tactilefeedback which indicates that the defined position, in this case thezero angle position, is reached.

Once a desired angular position has been found or reached, the rod 100is inserted until it rests on the support surface 65 of the pressuremember 6. The fixation member 7 is inserted between the legs 55 of thereceiving part and tightened so that the fixation member exerts pressureonto the rod and via the pressure member onto the head to lock theangular position of the head relative to the receiving part, as shown inFIG. 23b . The fixation member may have a protrusion 71 for pressing onthe rod while the legs 62 are not in contact with the fixation member.

In clinical use, at least two bone anchoring devices are inserted intobone and connected through a rod. The bone anchoring device according toembodiments of the invention can be used in a number of different ways.For example, the shank 2 may already be inserted into bone and thepre-assembled receiving part 5 with pressure member 6 and head 3 may bemounted onto the engagement portion of the shank in-situ. In anotheroption, in the configuration in which the head 3 and the pressure member6 are pre-assembled with the receiving part 5, the head can be mountedto the shank 2 prior to inserting the shank 2 into bone. Both optionsare useful, for example, when the shank is a large diameter shank whichcannot pass through the opening 51. If a shank is used that has asmaller outer diameter that can be guided through the opening 51, thehead 3 and the shank 2 can also be pre-assembled as shown in FIGS. 19ato 20c and guided through the receiving part 5 from the top end thereof,until the head 3 rests in the seat 52. Thereafter, the pressure member 6can be inserted and secured with the pins 4.

It shall be noted that various shanks can be used and connected to thehead and the receiving part so that the bone anchoring device canprovide a modular system which allows the use of many different shankscombined with the head and the receiving part.

When the shank is inserted into bone prior to mounting the receivingpart with pressure member and head thereon, the engagement portion 24 ofthe shank 2 provides the drive structure for engagement with a drivetool. Because the engagement portion is relatively large, higher torquescan be applied. On the other hand, once the bone anchoring device hasbeen fully assembled as shown in FIG. 22d , the drive structure 31 ofthe head 3 is also relatively large, so that higher torques can beapplied through the head 3. This can be useful for inserting the boneanchoring device in the configuration of FIG. 22d into the bone, forperforming corrections on the position of the shank in the bone, or whenthe bone anchoring device has to be removed completely.

FIG. 24 shows a modified embodiment of the bone anchoring device whichdiffers from the first embodiment shown in FIGS. 1 to 23 b in that itpermits pivoting of the bone anchoring element relative to the receivingpart at a larger maximum angle to one side compared to the oppositeside. The receiving part 5000 has a lower end 5 b′ in which a plane Pdefined by the opening 5100 extends in an inclined manner relative tothe central axis C. This can be manufactured, for example, by cutting anend portion of the receiving part at an angle. The seat 5200 for thehead is increased in the axial direction so that the seat providesenough support surface for the head 3 in the region with the enlargedpivot angle. As illustrated in FIG. 24, the bone anchoring element 1 ispivoted to one side at a larger maximum angle which may be limited by anabutment of a portion of the shank at the lower end 5 b′ of thereceiving part. It shall be noted that other geometries of the receivingpart and/or the shank may be provided that permit the shank to pivot ata greater maximum angle in one or more directions than in otherdirections.

A modular system can also be provided using different heads. As shown inFIG. 25, besides the head 3 as described above, another head 3′ with adifferent drive structure can be combined with the shank 2. Hence, sincethe bone anchoring device opens various options of assembly and use,such options can be further enlarged by adding various heads withdifferent properties, such as different drive structures, differentmaterials, different flexibility, or other properties to be selectivelycombined with a shank.

The head 3′ shown in FIG. 25 includes a drive structure 31′ that isidentical or similar to a Mortorq® drive. Depending on the size of thedrive structure 31′, the head 3′ can be used with the receiving part 5and the pressure member 6 of the first embodiment in an exchangeablemanner with the head 3.

The head 3′ can also be part of a second embodiment of the boneanchoring device as shown in FIGS. 26 to 37 c. Identical or similarparts and portions thereof are marked with the same reference numeralsas in the first embodiment, and the descriptions thereof will not berepeated. The bone anchoring device includes a bone anchoring element 1′having the shank 2 as in the first embodiment or another shank, the head3′, and a receiving part 5′. This embodiment differs from the firstembodiment in that the pressure member is not needed, so that the rod100 can transmit the pressure exerted by the fixation member 7 directlyonto the head 3′.

Referring to FIGS. 28 to 31, the head 3′ is substantially solid in theupper portion and has an outer spherical surface 30 a in the upperportion, with a radius that may be identical to the radius of thespherical outer surface 30 of the lower portion. In other words, thehead 3′ may have a substantially outer fully spherical surface except atthe second end 3 b, which may be substantially flat. In the uppersurface 30 a, the drive structure 31′ is provided in the form of agroove 31 a′ that forms wings or lobes that emanate from a center whichis coincident with the apex, i.e., the highest point on the sphericalupper surface 30 a in a curved manner. In greater detail, the groove 31a forms four wings 36 that are all curved towards the same side and havethe same shape and size and a regular distance. Such a design is knownas a Mortorq® drive. Each wing of the groove includes a substantiallystraight or slightly oblique section 36 a and a rounded section 36 b,wherein the two sections are connected at the tip of the wing. Thegroove 31 a′ is open at the tip of the wings 36 towards the outersurface, as can be seen in particular in FIG. 28. This kind of drivestructure is configured to transmit higher torques compared to variousother drive structure. The groove 33 and the engagement portion 34 arethe same as in the first embodiment. To enhance flexibility of the head3′, there may be a second, central recess 37 following the engagementrecess 34 in the direction towards the spherical upper surface 30 awhich has a smaller inner diameter so that the shoulder 34 a is formed.The slits 35′ may end at a distance from the groove 33 and may continueinto inner transverse slits 35 a, also for increased flexibility.However, the slits 35 and the central recess 37 cover the region withthe greatest outer diameter E of the head 3, so that the greatestdiameter of the head 3′ is slightly compressible towards the centralaxis C.

Referring to FIGS. 32 to 35 b, the receiving part 5′ has anaccommodation space 500 for the head 3′ in which the head 3′ can assumean insertion position and a final position for pivoting. To achievethis, the accommodation space 500 has near the second end 5 b a lowerseat 52′, more specifically a hollow spherical segment-shaped portionwith a radius matching the radius of the lower outer spherical surface30 of the head 3′. The height of the lower spherical seat 52′ is suchthat the lower seat 52′ extends slightly over the greatest outerdiameter E of the head 3′ when the head 3′ rests with the sphericalouter surface 30 in the lower seat 52′. By means of this, the head 3′ isheld in a pivot position by friction within the lower seat 52′. Thisprevents the head 3′ from being inadvertently kicked out of the lowerseat 52′ when it is in the pivot position and the rod and fixationmember are not yet inserted and fixed. The lower seat 52′ may widen witha small section 52 a′ towards the second end 5 b to facilitate insertionof the head 3′. The opening 51′ at the second end 5 b has a size suchthat the head 3′ can be introduced from the second end by compressingthe head slightly. In addition, the accommodation space 500 has an upperseat 520 that is separated from the lower seat 52′ by a circumferentialinner groove 510 which has a diameter greater than the largest diameterE of the head 3′. The inner groove 510 allows the head 3 ‘ to pass fromthe upper seat 520 into the pivot position in the lower seat 52’. Theupper seat 520 has a spherical shape matching the spherical shape of theouter surfaces 30 a, 30 of the head 3′ and is configured to receive anouter surface portion of the head 3′ which extends from the groove 33 tosome extent beneath the greatest diameter E when the head is in theupper seat 520. As the head 3 is somewhat compressible, the head can beheld in the upper seat 520 by friction. At an end of the upper seat 520towards the first end 5 a, an annular inner protrusion 521 is formedthat narrows the passage 50′. The protrusion 521 is configured to engagethe groove 33 when the head 3′ is in the upper seat 520. Moreover, theprotrusion 521 may have a flat bottom surface which faces the second end5 b to form a stop when engaging the groove 33 of the head 3′. By meansof the circumferential protrusion 521, the insertion position for thehead is defined. From the protrusion 521, the passage 50′ may widen to aregion with substantially constant diameter.

In this embodiment, a diameter of the inner thread 56 may be increasedcompared to the first embodiment to receive a slightly larger fixationmember. A groove in the inner wall below the thread as in the firstembodiment is not necessary, as this embodiment lacks a pressure member.It shall be noted that the recess 54′ for receiving the rod 100 has achannel diameter that substantially corresponds to the diameter of therod or is only slightly greater, so that the rod 100 is guided in therecess 54′. The size of the accommodation space 500 and the depth of thesubstantially U-shaped recess 54′ is such that when the head 3′ rests inthe lower seat 52′ in the pivot position, the apex of the upperspherical surface 30 a is above a bottom of the substantially U-shapedrecess 54′ in the axial direction to be engaged by a bottom surface ofthe rod 100 to exert pressure onto the head 3′ as shown for example inFIGS. 37b and 37 c.

The assembly of the head 3′ and the receiving part 5′ is illustrated inFIGS. 36a to 36d . First, as shown in FIG. 36a , the head 3′ is orientedsuch that the upper spherical surface 30 a faces towards the opening 51′of the receiving part 5′. The head 3′ is then introduced through theopening 51′ into the accommodation space 500. To achieve this, the head3′ is slightly compressed to pass through the opening 51′: As shown inFIG. 36b , the head 3′ can enter the upper seat 520 until the annularprotrusion 521 engages the lower portion of the groove 33, therebypreventing further upward movement. This is the insertion position forthe shank. The head 3′ is held in the upper seat 520 additionally byfriction, so that the head cannot move by itself out of the insertionposition into the pivot position. Thereafter, as depicted in FIG. 36c ,the shank 2 can be inserted with the engagement portion 24 spreadingapart the lower portion of the head 3′ to enter the recess of thecounterpart engagement portion 34. Finally, the engagement portion 24 ofthe shank 2 abuts against the stop 34 a and the shank 2 is held byfriction within the head 3′ as depicted in FIG. 36d . Due to the stopprovided by the annular protrusion 521, the head is prevented frommoving out of the receiving part in the direction towards the first end5 a during insertion of the shank.

Referring to FIGS. 37a to 37c , once the receiving part 5′ with head 3′is mounted to the shank 2, the head 3′ is moved out of the insertionposition into the lower seat 52′. As the protrusion 521 is roundedtowards the first end 5 a, the protrusion can easily move out of thegroove 33. In FIG. 37a , the axis of the shank 2 and the centrallongitudinal axis C of the receiving part 5′ are coaxial. Then, as shownin FIG. 37b , the receiving part 5′ can be pivoted relative to the shank2 and may be held in such a pivot position through friction in the lowerseat 52′. Finally, as depicted in FIG. 37c , the rod is inserted intothe substantially U-shaped channel 54′ and the fixation member 7 isscrewed between the legs 55 of the receiving part 5′. When the fixationmember 7 is tightened, the fixation member presses onto the rod and therod 100 presses in turn onto the spherical surface 30 a of the head 3′to lock the rod and the head.

It shall be noted that, as in the first embodiment, in clinical use, theshank can be first inserted into bone and the pre-assembled receivingpart 5′ with head 3′ can be mounted onto the shank, or alternatively,the bone anchoring device including the shank 2, the head 3′ and thereceiving part 5′ can be pre-assembled and then inserted into bone. Inany case, the drive structure 31′ is accessible to a tool through thepassage 50′ and provides a large drive surface for applying hightorques.

Further modifications of the above described embodiments are alsoconceivable. While the receiving part and the pressure member are shownas monolithic members, they can also be made up of two or more parts.For the shank all kinds of shanks can be used, such as partiallythreaded shanks, nails, cannulated shanks and various other shanks. Itmay be conceivable that the engagement portion of the shank has a recessand the counterpart engagement portion of the head includes a projectionfor engaging the recess of the shank. Various other drive structures forthe engagement portion of the shank or the drive structure of the headmay also be implemented.

The position indication structure can be designed so as to indicate apredefined angle other than the zero angle.

The pressure member may have legs that extend above the rod so that atwo-part fixation member can be used. In such a two-part fixationmember, for example, an inner fixation member is configured to act onthe rod and an outer fixation member is configured to act on the legs ofthe pressure member.

While the rod is shown as a cylindrical rod, the rod may also have anyother cross-section. The rod support surface can be cylindrical or flat,or have any other suitable contour for supporting the rod.

In addition, the particular features, structures or characteristics ofone embodiment may be combined with those of other embodiments in anysuitable manner to produce a multiplicity of further embodiments.Particular shapes of the elements are also not limited to the specificshapes shown in the drawings, but may vary as well.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

What is claimed is:
 1. An anchoring element comprising: a shank having afirst end and an opposite second end below the first end that isconfigured to anchor to bone, and a longitudinal axis that extendbetween the first and second ends; and a separate head that isconnectable around the first end of the shank, the head comprising anexterior surface with a spherically-shaped section and an unthreadedtool engagement surface that extends axially above an end face at thefirst end of the shank when the head and the shank are connected to oneanother for engaging a drive tool.
 2. The anchoring element of claim 1,wherein the shank comprises an engagement surface at the first endconfigured to selectively engage the head or a drive tool.
 3. Theanchoring element of claim 2, wherein the head comprises a first endwith the tool engagement surface, and an opposite second end comprisinga counterpart engagement surface for cooperating with the engagementsurface of the shank.
 4. The anchoring element of claim 1, wherein thetool engagement surface comprises a recess with a star-like ortorx-shaped structure.
 5. The anchoring element of claim 1, wherein whenthe head and the shank are connected to one another, the head comprisesa rounded free end surface on a side opposite to the shank, and whereinthe tool engagement surface comprises a groove formed around the freeend surface.
 6. The anchoring element of claim 5, wherein the groovecomprises a plurality of curved wings arranged around a center of thefree end surface.
 7. The anchoring element of claim 1, wherein the headcomprises a central axis, and wherein a portion of the head having agreatest diameter measured in a direction perpendicular to the centralaxis is compressible towards the central axis.
 8. A bone anchoringdevice comprising the anchoring element of claim 1, and a receiving partthat defines an accommodation space for receiving the head in apivotable manner.
 9. The bone anchoring device of claim 8, wherein thehead is connectable to the receiving part prior to connecting the shankto the head.
 10. The bone anchoring device of claim 9, wherein thereceiving part comprises an opening configured to permit at least aportion of the shank to extend therethrough for connecting to the head.11. The bone anchoring device of claim 8, wherein the head is configuredto assume an insertion position in the receiving part where the shank isconnectable to the head, and wherein the head is secured against axialmovement when at the insertion position.
 12. The bone anchoring deviceof claim 8, further comprising a pressure member configured to exertpressure on the head to lock the head in the accommodation space. 13.The bone anchoring device of claim 8, wherein the head is configured tobe locked in the accommodation space directly by a fixation member or arod.
 14. The bone anchoring device of claim 8, wherein the head is heldin the receiving part by friction.
 15. The bone anchoring device ofclaim 8, wherein the accommodation space comprises a seat for directlysupporting the head to permit the head to pivot, and wherein the head isheld by friction when in the seat.
 16. A bone anchoring devicecomprising: a shank for anchoring to bone; a separate head that isconnectable to the shank; and a receiving part that defines anaccommodation space configured to receive the head in a pivotablemanner; wherein when the head is in the receiving part at an insertionposition, the head is temporarily held at a first angular position andis restricted by an abutment against pivoting relative to the receivingpart to facilitate connection of the shank to the head; and wherein whenthe head is in the receiving part and when the shank is connected to thehead, the shank and the head are pivotable together relative to thereceiving part.
 17. The bone anchoring device of claim 16, wherein atthe first angular position, central axes of the head and the receivingpart are coaxial with one another.
 18. The bone anchoring device ofclaim 16, further comprising a pressure member configured to exertpressure on the head to lock the angular position of the head.
 19. Thebone anchoring device of claim 18, wherein the pressure member comprisesan engagement surface configured to releasably engage an engagementsurface at the head to hold the head relative to the pressure member atthe first angular position.
 20. An anchoring element comprising: a headcomprising a first end, an opposite second end, a longitudinal axisextending through the first and second ends, an end face at the firstend defining a first engagement surface that faces at least partiallycircumferentially around the longitudinal axis to engage a drive tool, asecond engagement surface at the second end that is different from thefirst engagement surface, and an exterior surface with aspherically-shaped section; and a separate shank configured to connectto the head along the longitudinal axis and to anchor to bone, the shankcomprising a third engagement surface that faces at least partiallycircumferentially around the longitudinal axis and that is configured toselectively engage a drive tool or the second engagement surface of thehead.